diff --git a/lib/compress.js b/lib/compress.js
index 21eec7c311..911cf55439 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1866,7 +1866,7 @@ merge(Compressor.prototype, {
                             return null;
                         }
                       default:
-                        return;
+                        return handle_custom_scan_order(node, multi_replacer);
                     }
                 }
                 // Replace variable when found
diff --git a/test/compress/collapse_vars.js b/test/compress/collapse_vars.js
index eaff0127cb..fcc47391b2 100644
--- a/test/compress/collapse_vars.js
+++ b/test/compress/collapse_vars.js
@@ -8897,3 +8897,38 @@ issue_4806: {
     }
     expect_stdout: "PASS"
 }
+
+issue_4852: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var a = "PASS";
+        (function(b) {
+            switch (b = a) {
+              case 42:
+                try {
+                    console;
+                } catch (b) {
+                    b.p;
+                }
+              case console.log(b):
+            }
+        })("FAIL");
+    }
+    expect: {
+        var a = "PASS";
+        (function(b) {
+            switch (a) {
+              case 42:
+                try {
+                    console;
+                } catch (b) {
+                    b.p;
+                }
+              case console.log(a):
+            }
+        })("FAIL");
+    }
+    expect_stdout: "PASS"
+}